Siliceous fiber for reinforcement and method of its manufacture

ABSTRACT

A plastic reinforcement of siliceous fibers, preferably glass of 4 to 5 microns diameter and 80 to 150 microns length, coated with a coupling agent. Short length siliceous fibers for reinforcing plastics are produced from blown wool by treating the wool with a coupling agent and mechanically separating the fibers by milling. When incorporated in plastic matrices, the fibers provide physical characteristics corresponding to or superior to more expensive drawn siliceous fibers having the same aspect ratio.

United States Patent Inventors James Ward Hyland, Jr.

Maumee; Roger Hill Bengtson, Whitehouse, both of O Appl. No. 23,416 Filed Mar. 27, 1970 Patented Nov. 2, 1971 Assignee Johns-Manville Corporation New York, N.Y.

SILICEOUS FIBER FOR REINFORCEMENT AND METHOD OF ITS MANUFACTURE [56] References Cited UNITED STATES PATENTS 3,480,456 11/1969 Forkner 241/23 X 3,519,211 7/1970 SakuIich et a1. 241/18 Primary ExaminerGranviIle Y. Custer, Jr. Attorneys-John A. McKinney and Robert M. Krone ABSTRACT: A plastic reinforcement of siliceous fibers, preferably glass of 4 to 5 microns diameter and 80 to 150 microns length, coated with a coupling agent. Short length siliceous fibers for reinforcing plastics are produced from blown wool by treating the wool with a coupling agent and mechanically separating the fibers by milling. When incorporated in plastic matrices, the fibers provide physical characteristics corresponding to or superior to more expensive drawn siliceous fibers having the same aspect ratio.

INTO WOOL MAT FIBER IAPPLY COUPLING AGENTI DIVIDE MAT CHARGE PARCELS INTO MILL MILL 0 ABC TO ABOUT IO WORKING FACES WITH ONE INCH SECONDS (OPTIONALLY) THAN ABOUT SEPARATE FINES HAVING ASPECT RATIO OF LESS PATENIEDIIIJV 2 IHTI FORM BLOWN INTO WOOL MAT FIBER [APPLY COUF LING AGENfl DIVIDE MAT INTO MILL CHARGE PARCELS MILL PARCELS DIAMETER OR ABOUT IG T FOR RESIDENC OF ABOUT TO ABOUT IO WITH LESS AT E TIME MINUTES SECONDS (OPTIONALLY) THAN ABOUT SEPARATE FINES HAVING ASPECT RATIO OF LESS I N VENTOIIS JAMES WARD HYLAND JR.

ROGER HILL BENGTSON ATTORNEY SILICEOUS FIBER FOR REINFORCEMENT AND METHOD OF ITS MANUFACTURE BACKGROUND OF THEINVENTION It has long been known that plastic matrices can be improved in their physical characteristics by incorporating siliceous fibers into the fluid mix. Such mixes have included chopped fibers and milled fibers. Chopped fibers have been derived from textile, or drawn or continuous filaments usually of about 13 to l4 microns diameter to lengths of from A to 1 inch. Milled fibers have been formed from continuous filament of about 13 to 14 microns diameter and a length of from 200 microns to 400 microns. In this type of reinforcing fiber a coupling agent such as a silane has been applied to enhance the physical properties of the resulting plastic-fiber matrix. Blown fibers have also been employed in milled form, however, it has been observed that the milled fibers have a wide variation in size with a substantial portion of the end product in powder form in which the particle length is of the same magnitude as the fiber diameter, and thus offer a minimum of matrix reinforcement. When untreated, milled blown fiber was used in plastic matrices, inferior physical properties including low-Izod impact strength, high-water absorption, lowflexural strength and low-fiexural modulus relative to milled textile fibers of both the untreated and the coupling agent treated type. Attempts to treat blown fibers with coupling agents and mill the fibers according to prior techniques resulted in clumping and balling of the material into large masses which were not useable as reinforcing agents.

SUMMARY OF THE INVENTION This invention relates to a method of milling blown siliceous fibers to provide a high yield of uniform-sized reinforcing fibers. It further enables blown siliceous fibers to be treated with a coupling agent and be milled to a useful product of comparable reinforcing capability of prior art milled continuous filament fibers.

An object of the invention is reduction of the cost of milled fibers.

Another object is to enable inexpensive blown fibers to be milled to form a reinforcing agent of a quality comparable or even superior to milled continuous filament.

A third object is to increase production rates of milled blown fibers.

A fourth object is to enable blown fibers which have been treated with a coupling agent to be milled.

A fifth object is to mill friable fibers to a relatively high yield of relatively uniform useful reinforcing length.

In accordance with the above objects, a feature of this invention resides in rapidly reducing blown fiber by ball milling with a limited milling period. In batch milling in a ball mill, a maximum of /z hour has been employed with optimum yields achieved in about liminutes. Continuous vibritory ball mills have been employed advantageously with dwell times of the order of 15 seconds.

Another feature resides in the ball milling of fibers treated with coupling agents appropriate for the plastic in which they are to be employed as a reinforcement agent.

DESCRIPTION OF THE DRAWING The DRAWING is a flow chart of an in-line process of producing the milled, coupling agent coated, fine diameter siliceous fibers of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Heretofore reinforcing glass fibers for plastics have been formed in short lengths by both chopping and milling continuous filament fibers which have been coated with a coupling agent suitable for the particular plastic to be reinforced. Reinforcement is in large measure dependent upon two factors, the surface bond between the fiber and the plastic, and the length of the fiber as related to its diameter. Limits are imposed on fiber length where it is dispersed in the fluid plastic and then applied since a uniform distribution of the fibers throughout the plastic is desirable. In the case of milled fibers a length to diameter ratio, the aspect ratio, of 20:1 to 30zl is highly desirable for effective reinforcement. Such aspect ratios have been achieved starting with continuous filament in both uncoated and coated form. These fibers are usually l3 to 14 microns in diameter, and therefore, from 200 to 400 microns in length where the aspect ratio of 20:1 to 30zl is maintained. Attempts have been made to achieve finer diameter reinforcing fibers.

In the case of glass fibers, a high-velocity gas blast, as steam or flame imposed upon the fibers drawn through small orifices attenuate the filaments into an essentially random dispersal of fibers in a wool like mass or mat. These fibers, tenned "blown fibers, are usually of 4 or 5 microns diameter. While they provide an excellent starting material for fine diameter reinforcing fibers, it was found that blown fibers tended to be so friable that an uneconomical yield of fibers with an aspect ratio of 20:1 to 30:1 was experienced. Much of the material was reduced to powder where the aspect ratio was 3 or less. It had not been possible to apply coupling agents to the blown fiber since the fibers required coating prior to milling process caused balling of the coated fibers. Such balled masses of fiber were of no utility as reinforcement.

The present invention involves a mass of fibers of 4 or 5 microns diameter coated with a coupling agent and falling in a range of aspect ratios of 20:l to 30:1 with respect to about percent of the fibers. This new product is produced less expensively than milled, coated, continuous filament fibers and offers greater reinforcement for a given weight of glass in a plastic matrix.

While the preferred application of the process of this invention is to blown glass fibers and particularly such fibers of borosilicate glass, it is to be understood that it is applicable to other inorganic fibers which are available in random lengths and orientation as wool matt and the like. Glass fibers are formed with fine and relatively uniform diameters in blown or other known attenuation processes at low cost. Other materials which can be fiberized as by usual means of spinning, drawing, attenuating and blowing into fine diameter fiber can be employed exclusively or in part in the formation of the mat to which this process is applied. These may include known products manufactured from various source materials of silicates of metal oxides, such as rock wools from argillaceous matter or shale, slag wool from metallurgical slags, each commonly referred to as mineral wools," aluminum silicate fibers, and any fibers of the so-called glasses.

It has long been known to employ coupling agents with textile fibers and to match those agents to the plastic matrix in which the fibers are to be incorporated. One means of applying these agents is to draw the filaments across a coating wheel or through a spray of the agent. Typically continuous glass filaments for use with thermoplastics are coated with gamma amino propylsilane while glass filaments for reinforcement in polyesters are coated with a vinyl silane. In the case of glass wool mat which is collected after attenuation into small lengths of individual fine fibers on a moving formation conveyor, the coupling agent can be applied in a solution in water or an emulsion of suspension, typically by spraying the mat although fogging and immersion can also be employed.

In the past, mat of coated blown fiber could not be milled to a product commercially acceptable for plastic reinforcement. Further, when coated blown fiber was milled by conventional techniques, suitable for continuous glass filaments the blown glass fibers were in large part reduced to a length of the order of their diameter rather than the desired length to diameter or aspect ratio of 20:1 to 30:1. Attempts were made to process glass wool in hammer mills which effectively chopped the wool with rotating knives. The glass wool coated with a coupling agent could not be reduced to the desired lengths of individual fibers with sufficient uniformity to be of practical value. Accordingly, the glass wool was subjected to a two-step process involving a batch charge to a hammer mill followed by the processing of the milled charge in a pan crusher or muller. This also resulted in a wide range of fiber size and the aforenoted balling of fibers although the length of the fibers were reduced sufliciently. The two-step process was practiced with a low yield on blown glass fibers which had no coupling agent. The resultant product is produced at high cost with substantial loss when subjected to final separation as by screening to eliminate the undesirable fines.

According to the present invention, a suitable coupling agent is applied to blown glass fiber wool mat as by spraying from sprayheads as it is picked up by a forming bed. The mat of coated fibers is then delivered to a suitable mechanism for dividing it into parcels for charging to a mill. A commercial comminuting mill can be employed for this purpose whereby the wool is forced through a screen having 1 inch-diameter apertures. The resultant parcels when relieved of the compressive forces of the mill expand to maximum dimensions of about 2 inches. They then are fed to a ball mill for final milling to size.

While batch charges of the aforementioned blown glass can be processed in small quantities in a batch-type rotary ball mill it is advantageous where a high rate of production is sought for commercial economy to employ a continuous vibratory ball mill. More particularly, silane-coated blown glass has been milled in 30 pound batches in a rotary ball mill with a milling interval of 15 to 30 minutes to produce a commercially acceptable product. The mill employed had a diameter of 36 inches and a length of 60 inches. Various milling media including steel balls, porcelain spheres, and natural stone spheres have been employed.

It is theorized that ball milling works the material more intensively over a shorter period and with less heat generation than the hammer mill and muller process to produce the high yields of 4 to 5 micron, silane-coated fibers having an aspect ratio of 20:1 to 301i. A gravity or tumbling-type ball mill is limited in the degree of working to gravitational forces modified by the constraints of the release of the balls at their angle of repose with the walls of the milling chamber. A substantial improvement in processing has been achieved by employing a more intense milling.

Production rates of 1,200 pounds per hour are available by employing a continuous vibratory ball mill having a cylindrical chamber inches in diameter and 18 inches long operated at about 1,200 cycles per minute with a ifs-inch throw. In this mill, much of the working is between the agitated balls which occupy approximately 80 percent of the grinding chamber volume. Steel, porcelain and stone grinding media have been employed. This milling imparts forces to the charge of up to fifteen times gravity and thus fifteen times that available in the tumbling-type mill. When these intense forces are applied to the friable blown glass fibers, the time of application must be curtailed to avoid over milling as to an aspect ratio of 1. In particular, a dwell time for the material in a mill having a l,200 pound per hour throughput has been about 15 seconds. As a result, a high yield of milled fibers in the aspect ratio range desired, between 20 and is achieved and the material issuing from the mill is cool enough to be comfortably handled with bare hands, it is essentially at room temperature as it issues. Thus no tackiness is developed in the coupling agent coating and the fibers do not ball.

The blown fiber is a less-expensive product than the drawn attenuated continuous filament as a starting material since the raw glass can be less expensive and the forming process is less expensive. it is easily and economically coated as the continuous filament. It can be milled in the continuous vibratory ball mill much more inexpensively than either chopped continuous filament or milled continuous filament. When coated, its physical properties as a reinforcement for plastics are comparable to the more expensive chopped and milled continuous filament material.

The process lends itself to an in line" production wherein,

as shown in the drawing, the process is practiced as a continuous series of steps involving forming the blown fiber into a wool mat, applying the coupling agent, dividing the mat of coated fibers into suitable charge increments for the mill, milling the mat of coated fibers, and, optionally, separating fines from the milled mass as by screening. in the screening process, it has been found that the fines, those fibers having an aspect ratio of about three or less, constitute only about 5 percent by weight of the original charge.

It is contemplated that the present process could be adapted to mills other than ball mills provided the mat of blown and coated siliceous fiber wool is worked over small areas, as in the case of balls of from 1 inch to about V4 inch diameter, with forces of the order of 1G to 150, and for brief intervals such as from about 10 seconds residence time to about 30 minutes where working force and residence time are inversely related. Accordingly, it is to be understood that variations from the disclosed process are evident and can be made without departing from the spirit and scope of the invention. The above disclosure should, therefore, be read as illustrative and not in a limiting sense.

What is claimed is:

l. The method of forming reinforcing fibers for dispersal in a matrix comprising the steps of applying a coupling agent to blown siliceous fibers in a mat, and milling the mat of fibers to which the coupling agent has been applied in a ball mill.

2. The method according to claim 1 wherein said milling is performed in a vibratory ball mill operated to impart from i to 15 G to its grinding media and charge of the fibers.

3. The method according to claim 2 including the step of milling the fibers for about 15 seconds.

4. The method according to claim 1 including the step of milling the fibers for from about l0 seconds to about 30 minutes.

5. The method according to claim 1 wherein said milling is performed in a tumbling-type ball mill for an interval of about 20 to 30 minutes.

6. The method according to claim 1 wherein the milling balls are from about 1 inch in diameter to about V inch in diameter.

7. The method according to claim 1 wherein the milling is performed in a continuous vibratory ball mill vibrated at about 1,200 cycles per minute with a throw of up to "74 of an inch.

8. The method according to claim 7 wherein the balls fill about percent of the mill volume.

9. The method according to claim 8 wherein the balls are steel of from about 1 inch to about wa-inch diameter.

10. The method according to claim 9 wherein the residence time of fibers in the mill is about 15 seconds.

11. The method according to claim 1 including the step of producing the siliceous fibers by passing filaments of glass through a high-velocity gas stream to attenuate the fibers to about 4 to 5 microns diameter, and wherein the coupling agent is a silane.

12. The method according to claim 1 including the step of separating fines having an aspect ratio of less than about 3 from the milled product.

13. The method according to claim 1 including the step of forming discrete bodies of siliceous mat of a size to be conveniently charged into the mill.

14. The method offorming reinforcing fibers for dispersal in a matrix comprising the steps of applying a coupling agent to blown siliceous fibers in a mat, milling the mat of fibers to which the coupling agent has been applied with a working surface of less than 1 inch diameter subjected to forces of from I to 15 G for a period of from l0 seconds to about 30 minutes with the period an inverse function of the forces imparted to the working surface.

15. A reinforcing mass of siliceous fibers comprising filaments averaging 4 to 5 microns in diameter and having a ratio of length to diameter of 20:1 to 30:1 and a coating of a silane coupling agent on said fibers. 

2. The method according to claim 1 wherein said milling is performed in a vibratory ball mill operated to impart from 1 to 15 G to its grinding media and charge of the fibers.
 3. The method according to claim 2 including the step of milling the fibers for about 15 seconds.
 4. The method according to claim 1 including the step of milling the fibers for from about 10 seconds to about 30 minutes.
 5. The method according to claim 1 wherein said milling is performed in a tumbling-type ball mill for an interval of about 20 to 30 minutes.
 6. The method according to claim 1 wherein the milling balls are from about 1 inch in diameter to about 1/4 iNch in diameter.
 7. The method according to claim 1 wherein the milling is performed in a continuous vibratory ball mill vibrated at about 1,200 cycles per minute with a throw of up to 3/4 of an inch.
 8. The method according to claim 7 wherein the balls fill about 80 percent of the mill volume.
 9. The method according to claim 8 wherein the balls are steel of from about 1 inch to about 1/4 -inch diameter.
 10. The method according to claim 9 wherein the residence time of fibers in the mill is about 15 seconds.
 11. The method according to claim 1 including the step of producing the siliceous fibers by passing filaments of glass through a high-velocity gas stream to attenuate the fibers to about 4 to 5 microns diameter, and wherein the coupling agent is a silane.
 12. The method according to claim 1 including the step of separating fines having an aspect ratio of less than about 3 from the milled product.
 13. The method according to claim 1 including the step of forming discrete bodies of siliceous mat of a size to be conveniently charged into the mill.
 14. The method of forming reinforcing fibers for dispersal in a matrix comprising the steps of applying a coupling agent to blown siliceous fibers in a mat, milling the mat of fibers to which the coupling agent has been applied with a working surface of less than 1 inch diameter subjected to forces of from 1 to 15 G for a period of from 10 seconds to about 30 minutes with the period an inverse function of the forces imparted to the working surface.
 15. A reinforcing mass of siliceous fibers comprising filaments averaging 4 to 5 microns in diameter and having a ratio of length to diameter of 20:1 to 30:1 and a coating of a silane coupling agent on said fibers. 